It really depends. Beginning Nathan vs. Beginning Soma: Nathan wins due to the fact that he is a trained warrior whereas Soma has few, if any, and no experience. Late-Game Nathan vs. Late-Game Soma (not the Dark Lord): it a toss up. Nathan has the training and the DSS. Soma has a lot of abilities from the souls he's absorbed. Nathan has the Unicorn+Pluto combo which makes him invincible, but it eats up a lot of power that takes time to regenerate. If Soma has the Chaos Ring, he will have an infinite supply of power. If Soma doesn't have the ring, Nathan should have a slight advantage even if they both run out of power. If Soma has the ring, he will have the advantage. Especially, if we are talking about AoS Soma who can heal himself. Infinite supply of magic+the ability to self heal = advantage Soma.